An isochoric process , also called a constant-volume process , an isovolumetric process , or an isometric process , is a thermodynamic process during which the volume of the closed system undergoing such a process remains constant. An isochoric process is exemplified by the heating or the cooling of the contents of a sealed, inelastic container: The thermodynamic process is the addition or removal of heat; the isolation of the contents of the container establishes the closed system; and the inability of the container to deform imposes the constant-volume condition. The isochoric process here should be a quasi-static process.

The solution of Equation given below for a constant volume process is also not difficult. The work done in a constant volume process is the product of the volume and the change in pressure.

In addition to gases, Equation 1-45 also applies to liquids. The power requirement for pumps that move incompressible liquids (such as water) can be determined from Equation 1-44. Replacing the volume (V) with the product of the specific volume and the mass yields Equation 1-45.

Taking the time rate of change of both sides of Equation 1-46 determines the power requirements of the pump.